1. Field of the Invention
The present invention relates to a structure of a toroidal core type actuator and more particularly the stator structure of the toroidal core type actuator which facilitates winding and mounting and enables reduction in costs.
2. Description of the Prior Art
A toroidal core type actuator is designed so that rotating shaft operates in repetitive rotary motions. While the repetitive rotary motions are within range of 180.degree. (.+-.90.degree.), it is desired to produce constant torques in the range of the operational angle. In other words, the actuator is required for characteristics that the torques produced have no angle dependence at identical currents. With this view, so-called toroidal core type actuator constitution is typically employed in which wires are wound in coils about the circumference of a hollow cylindrical core to prepare a stator and a rotor comprising a permanent magnet is rotatably arranged in the hollow cylindrical core via a minute air gap.
However, since the hollow cylindrical core is used as the winding core when winding the coils about the circumference thereof, a special winding machine is naturally required for the toroidal core type actuator. This not only causes complication of the winding process, but also produces a drawback that collapse of the convolutions of the coils, and terminal handling after winding, positioning of the stator and the rotor after winding, fixing thereof and the like become problems to hamper stable constitution of the stator unit with excellent working properties.
Moreover, since the hollow cylindrical core requires a constant permeance (reciprocal of reluctance) along the circumferential direction, high dimensional accuracies are needed of the core. On this account, the stator is constituted by machining a block material, or by punching flat rolled soft magnetic steel strips having insulated surfaces into a disc shaped one under a press and then laminating the same in an axial direction. The machining, while securing high dimensional accuracies, produces a problem in increasing work costs. The lamination method requires expensive molds, and has problems in caulking accuracies and the like. Thus, there has been needed a stator structure which can be constituted at lower costs.